Iron(III) complexes promote hydrogen peroxide activation for efficient degradation of dyeing wastewater

Coordination complexes were widely used in advanced oxidation processes. The ligands with various substituents could lead to differences in the catalytic properties and mechanisms. In this work, the iron(III)–N,N′-dipicolinamide (FeL) complexes (the iron(III) complexes with substituents –CH₃, –H, –Cl and –NO₂ named as FeL1, FeL2, FeL3 and FeL4, respectively) were used to activate hydrogen peroxide (H₂O₂) for degrading dyes wastewater. Mechanism studies indicated that the FeL4/H₂O₂ system contains the Fe^V=O in addition to the same ^•OH and O₂^•− as the other systems, which made it exhibit more excellent performance than others. The results of the performance tests showed that the FeL4/H₂O₂ system could remove 97%, 89%, 100%, 83%, 100%, and 99% of RR195, RY145, RB194, RB19, MB, and RhB, respectively, which proved the good application performance of the FeL4/H₂O₂ system. In addition, the performance of the FeL4/H₂O₂ system was not influenced by anions and natural organics. This study verified the feasibility of modulating the catalytic performance of the complexes by changing the substituents and provided an efficient catalytic system for dyeing wastewater treatment.